Radamel Falcao will silence those who doubt his fitness, says Rodriguez.Getty Images/Alex Livesey

Real Madrid star James Rodriguez is confident Manchester United striker Radamel Falcao will silence those who question his long-term fitness.

Falcao, on a season-long loan from Monaco, has missed United's last three games due to a calf problem and is also a doubt for the clash with Arsenal which follows the international break.

Having missed the second half of last season and the summer's World Cup due to a serious knee injury, the striker's latest struggles have prompted concern over his long-term fitness.

The Colombian international moved to dismiss such concerns last week and his compatriot Rodriguez believes it is only a matter of time before the 28-year-old rediscovers his lethal touch.

"I've not had the chance to speak with him yet, but he has to stay calm and he's mentally strong," Rodriguez said ahead of Colombia's international friendly with USA. "We all have our critics, but he's going to get through this. He'll be fine and will start scoring goals to shut all their mouths."

Falcao's last appearance for United came off the substitutes' bench against West Bromwich Albion on 20 October. He has missed key clashes against Chelsea and Manchester City because of injury.

Given his prolonged absence, his manager Louis van Gaal indicated this week that a starting role against Arsene Wenger's side at the Emirates later in the month is unlikely, although a spot on the bench is a possibility.

"They (referring to Falcao, Rafael da Silva, Jonny Evans and Phil Jones) could sit on the bench because they can play 20 minutes but I cannot put a lot of players who are not 100 percent fit on the bench," van Gaal said.

"You saw what happened with [Paddy] McNair [who suffered from cramp against Crystal Palace] because the rhythm of the game is very high in the Premier League."